Here’s the alarmists’ thought process: Where’s the missing heat? Our models must be right (no doubt there), so it must be hiding somewhere. Somewhere we can’t measure it. Deep in the oceans!
And because of the much larger heat capacity of water compared to air, the differences in temperature would be of the order of hundredths of a degree. Which is conveniently impossible to measure accurately.
Which is why ocean heat content is the buzzword du jour…